The present invention relates generally to a heater control apparatus, and more particularly to a heater control apparatus for use with a plurality of printers connected to a host computer, which prevents two or more heaters of the plurality of printers from being turned ON so that the plurality of printers are kept from overload.
Conventionally, a halogen heater having a rated power load ranging from 500 W to 1000 W is commonly used as a fixing heater in a printer connected to a host computer including a personal computer. This fixing heater is provided for heating a fixing roller of the printer, and the fixing roller is heated when the fixing heater is turned ON at appropriate timings so that a surface of the fixing roller is maintained to a constant, suitable temperature. Although it is common that a single printer is connected to a personal computer, there are cases in which a plurality of printers connected to a host computer are installed in an office for business use. The printers of the type described above usually require a consumption current ranging from 5 A to 10 A while electric power from a commercial power supply of a rated voltage of 100 V a.c. is used. However, a normal power supply of a power distribution system for office use supplies the rated current of 20 A. Accordingly, in a case in which a plurality of printers are installed in an office for use with a host computer, it is necessary to reduce the number of printers being installed such that the total of consumption currents by the plurality of printers in operation falls within the range of permissible current which is supplied by such a normal power supply so as to prevent the above described overload problem from taking place due to several heaters of the printers being turned ON at the same time. Otherwise, it is necessary to change an office wiring construction so that the power supply may supply normally a greater capacity of the rated current to enable the plurality of printers connected to a host computer to be used without rendering the above described overload.
One conceivable method to eliminate the above described problem is to use a common signal line through which a plurality of printers are coupled one another to monitor the operating condition of each heater in the plurality of printers by checking the ON/OFF state of a request signal presented on the common signal line. This request signal is supplied from one printer among the printers when the heater of this printer is turned ON for heating the fixing roller of the printer being considered, so as to present to other printers the "ON" state of the heater of the printer being considered. However, the heaters of the printers are individually controlled by the respective printer controllers thereof so that the respective heaters are turned on and off separately at appropriate timings for maintaining a surface of the fixing roller of each printer constantly to a given suitable level. Thus, even if the above mentioned method is applied, there still remains a possibility that two or more heaters of the printers are turned ON simultaneously, thus rendering the overload problem, and the reliability of the printers connected to a host computer is still not at a sufficient level.